From 16e416b8d745b1fc64111581fec431d843591274 Mon Sep 17 00:00:00 2001
From: Benoit Jacob <jacob.benoit.1@gmail.com>
Date: Tue, 30 Mar 2010 14:47:45 -0400
Subject: [PATCH] generalize the idea of the previous commit to all kinds of
 casts, see this forum thread: http://forum.kde.org/viewtopic.php?f=74&t=86914
 this  is important to allow users to support custom types that don't have the
 needed conversion operators.

---
 Eigen/src/Core/IO.h            |  2 +-
 Eigen/src/Core/MathFunctions.h | 13 ++++++++-----
 2 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/Eigen/src/Core/IO.h b/Eigen/src/Core/IO.h
index 22db103ed..c98742246 100644
--- a/Eigen/src/Core/IO.h
+++ b/Eigen/src/Core/IO.h
@@ -132,7 +132,7 @@ struct ei_significant_decimals_impl
   typedef typename NumTraits<Scalar>::Real RealScalar;
   static inline int run()
   {
-    return ei_cast_to_int(std::ceil(-ei_log(NumTraits<RealScalar>::epsilon())/ei_log(RealScalar(10))));
+    return ei_cast<RealScalar,int>(std::ceil(-ei_log(NumTraits<RealScalar>::epsilon())/ei_log(RealScalar(10))));
   }
 };
 
diff --git a/Eigen/src/Core/MathFunctions.h b/Eigen/src/Core/MathFunctions.h
index 943b44cfa..4a21ec975 100644
--- a/Eigen/src/Core/MathFunctions.h
+++ b/Eigen/src/Core/MathFunctions.h
@@ -44,17 +44,20 @@ template<typename T> inline typename NumTraits<T>::Real ei_hypot(T x, T y)
   return p * ei_sqrt(T(1) + qp*qp);
 }
 
-template<typename T> struct ei_cast_to_int_impl
+// the point of wrapping these casts in this helper template struct is to allow users to specialize it to custom types
+// that may not have the needed conversion operators (especially as c++98 doesn't have explicit conversion operators).
+
+template<typename OldType, typename NewType> struct ei_cast_impl
 {
-  static int run(const T& x)
+  static inline NewType run(const OldType& x)
   {
-    return int(x);
+    return static_cast<NewType>(x);
   }
 };
 
-template<typename T> inline int ei_cast_to_int(const T& x)
+template<typename OldType, typename NewType> inline NewType ei_cast(const OldType& x)
 {
-  return ei_cast_to_int_impl<T>::run(x);
+  return ei_cast_impl<OldType, NewType>::run(x);
 }